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November 5, 2014, 08:22 |
Floworks and airfoil drag coefficient
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#1 |
New Member
Join Date: Oct 2012
Posts: 3
Rep Power: 13 |
Hello,
I am trying to use Floworks to evaluate the lift and drag coefficients of an airfoil. While the computed lift coefficients match more or less the expected values, the computed drag coefficients are much higher than the expected ones (>2 x the expected ones). Is Floworks suited to do that sort of computations? If yes and if i post the details of my calculation setups, can someone help me to find out what I am doing wrong? Thanks! |
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November 5, 2014, 17:20 |
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#2 |
Disabled
Join Date: Jul 2009
Posts: 616
Rep Power: 23 |
Yes, it is possible to do such simulations. The important thing is a correct meshing and solver selection (eventually high mach number option) depending on your flow velocity etc.
Boris |
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November 6, 2014, 03:18 |
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#3 |
New Member
Join Date: Oct 2012
Posts: 3
Rep Power: 13 |
Hello Boris, thank you for your reply.
The simulation setup is pasted below. I have attached an image of the initial mesh around the airfoil and another one showing the mesh after a level 3 refinement during the computation. I've got a glide ratio Fw/Fa = 0,055, which is far too high given the high Reynolds number (>10^6). I have tried other setups before, but the results were even worse. I can't really figure out how to fix that. INPUT DATA Initial Mesh Settings Automatic initial mesh: Off Basic Mesh Dimensions Number of cells in X: 121 Number of cells in Y: 77 Number of cells in Z: 1 Control Planes Control planes in X direction Name Minimum Maximum Number of cells Ratio X1 -1.850 -0.175 - 6.4238891 X2 -0.175 0.035 - 1.0000000 X3 0.035 0.381 - 1.0000000 X4 0.381 2.750 - 0.1150187 Control planes in Y direction Name Minimum Maximum Number of cells Ratio Y1 -1.250 -0.047 - 5.5625441 Y2 -0.047 -0.010 - 1.0000000 Y3 -0.010 0.027 - 1.0000000 Y4 0.027 1.150 - 0.1902753 Control planes in Z direction Name Minimum Maximum Number of cells Ratio Z1 -0.001 0.001 - 1.0000000 Solid/Fluid Interface Small solid features refinement level: 7 Curvature refinement level: 7 Curvature refinement criterion: 0.010 rad Tolerance refinement level: 7 Tolerance refinement criterion: 0.001 m Refining cells Refine fluid cells: Off Refine partial cells: Off Refine solid cells: Off Narrow Channels Advanced narrow channel refinement: On Characteristic number of cells across a narrow channel: 5 Narrow channels refinement level: 7 The minimum height of narrow channels: Off The maximum height of narrow channels: Off Computational Domain Size X min: -1.850 m X max: 2.750 m Y min: -1.250 m Y max: 1.150 m Z min: -0.001 m Z max: 0.001 m Boundary Conditions 2D plane flow: XY - plane flow At X min: Default At X max: Default At Y min: Default At Y max: Default At Z min: Symmetry At Z max: Symmetry Physical Features Heat conduction in solids: Off Time dependent: On Gravitational effects: Off Flow type: Laminar and turbulent Cavitation: Off High Mach number flow: Off Default roughness: 0 micrometer Default wall conditions: Adiabatic wall Ambient Conditions Thermodynamic parameters Static Pressure: 101325.00 Pa Temperature: 283.00 K Velocity parameters Velocity vector Velocity in X direction: 9.650 m/s Velocity in Y direction: 0 m/s Velocity in Z direction: 0 m/s Turbulence parameters Turbulence intensity and length Intensity: 0.10 % Length: 1.000e-004 m Material Settings Fluids Water Goals Global Goals GG Min Static Pressure Type: Global Goal Goal type: Static Pressure Calculate: Minimum value Coordinate system: Global coordinate system Criteria: 100.00 Pa Use in convergence : On GG Av Density (Fluid) Type: Global Goal Goal type: Density (Fluid) Calculate: Average value Coordinate system: Global coordinate system Criteria: 100.00 kg/m^3 Use in convergence : On GG Max Velocity Type: Global Goal Goal type: Velocity Calculate: Maximum value Coordinate system: Global coordinate system Criteria: 0.010 m/s Use in convergence : On GG Force (X) Type: Global Goal Goal type: Force (X) Coordinate system: Global coordinate system Criteria: 1.000 N Use in convergence : On GG Force (Y) Type: Global Goal Goal type: Force (Y) Coordinate system: Global coordinate system Criteria: 1.000 N Use in convergence : On Equation Goals Za Type: Equation Goal Formula: GG Force (Y) *2/1000/9,65/9,65/0,378/0,002 Dimensionality: No units Criteria: 0.0001000 Use in convergence : On Zw Type: Equation Goal Formula: GG Force (X) *2/1000/9,65/9,65/0,378/0,002 Dimensionality: No units Criteria: 1.0000000e-005 Use in convergence : On tanL Type: Equation Goal Formula: GG Force (X) /GG Force (Y) Dimensionality: No units Criteria: 1.0000000e-008 Use in convergence : On Calculation Control Options Finish Conditions Finish conditions: If one is satisfied Goals convergence Analysis interval: 3e-001 Solver Refinement Refinement: Disabled Results Saving Save before refinement: On Advanced Control Options Flow Freezing Flow freezing strategy: Disabled Manual time step (Freezing): Off Manual time step: 0.003 s mesh1.jpg mesh after refinement.jpg |
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November 6, 2014, 14:59 |
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#4 |
Disabled
Join Date: Jul 2009
Posts: 616
Rep Power: 23 |
Yes, that's not a good way of setting a project up for such an application. Don't use small feature refinement like that. Also use more local meshes and don't change the angle of the airfoil but use the capability of defining the aerodynamic angle in the initial conditions of the project.
If you send me your email address in a private message I can send you some more information and examples. Boris |
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November 14, 2014, 09:45 |
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#5 |
New Member
Join Date: Oct 2012
Posts: 3
Rep Power: 13 |
Hello,
adjusting the computational domain size and he mesh has actually shown to be crucial to obtaining realistic results. In the simulation setup pasted below, as suggested by Boris docs, the computational domain size is more than 20 times larger than the chord length in each direction. A local mesh around the airfoil has been shaped like in the attached image. The "aerodynamic angles" feature of FW 2014 has been used (velocity: 9,65 m/s; angle of attack: 5°) INPUT DATA Initial Mesh Settings Automatic initial mesh: On Result resolution level: 6 Advanced narrow channel refinement: On Refinement in solid region: Off Geometry Resolution Evaluation of minimum gap size: Automatic Evaluation of minimum wall thickness: Automatic Local Mesh Settings Mesh locale Components: Mesh locale-1 Solid/fluid interface Small solid features refinement level: 3 Curvature refinement level: 3 Curvature refinement criterion: 0.100 rad Tolerance refinement level: 3 Tolerance refinement criterion: 0.010 m Refining cells Refine all cells: On Level of refining all cells : 0 Narrow channels Advanced narrow channel refinement: On Characteristic number of cells across a narrow channel: 14 Narrow channels refinement level: 3 The minimum height of narrow channels: Off The maximum height of narrow channels: Off Computational Domain Size X min: -10.000 m X max: 15.000 m Y min: -15.000 m Y max: 10.000 m Z min: -0.001 m Z max: 0.001 m Boundary Conditions 2D plane flow: XY - plane flow At X min: Default At X max: Default At Y min: Default At Y max: Default At Z min: Symmetry At Z max: Symmetry Physical Features Heat conduction in solids: Off Time dependent: Off Gravitational effects: Off Flow type: Laminar and turbulent Cavitation: Off High Mach number flow: Off Default roughness: 0 micrometer Default wall conditions: Adiabatic wall Ambient Conditions Thermodynamic parameters Static Pressure: 101325.00 Pa Temperature: 283.00 K Velocity parameters Velocity vector Velocity in X direction: 9.650 m/s Velocity in Y direction: 0 m/s Velocity in Z direction: 0 m/s Turbulence parameters Turbulence intensity and length Intensity: 0.10 % Length: 1.000e-004 m Material Settings Fluids Water Goals Global Goals GG Min Static Pressure Type: Global Goal Goal type: Static Pressure Calculate: Minimum value Coordinate system: Global coordinate system Criteria: 100.00 Pa Use in convergence : On GG Av Density (Fluid) Type: Global Goal Goal type: Density (Fluid) Calculate: Average value Coordinate system: Global coordinate system Criteria: 100.00 kg/m^3 Use in convergence : On GG Max Velocity Type: Global Goal Goal type: Velocity Calculate: Maximum value Coordinate system: Global coordinate system Criteria: 0.010 m/s Use in convergence : On GG Force (X) Type: Global Goal Goal type: Force (X) Coordinate system: Sistema di riferimento pala Criteria: 1.000 N Use in convergence : On GG Force (Y) Type: Global Goal Goal type: Force (Y) Coordinate system: Sistema di riferimento pala Criteria: 1.000 N Use in convergence : On Equation Goals Za Type: Equation Goal Formula: GG Force (Y) *2/1000/9,66/9,66/0,39/0,002 Dimensionality: No units Criteria: 0.0001000 Use in convergence : On Zw Type: Equation Goal Formula: GG Force (X) *2/1000/9,66/9,66/0,39/0,002 Dimensionality: No units Criteria: 1.0000000e-005 Use in convergence : On tanL Type: Equation Goal Formula: GG Force (X) /GG Force (Y) Dimensionality: No units Criteria: 1.0000000e-008 Use in convergence : On Calculation Control Options Finish Conditions Finish conditions: If one is satisfied Goals convergence Analysis interval: 5e-001 Solver Refinement Refinement: Disabled Results Saving Save before refinement: On Advanced Control Options Flow Freezing Flow freezing strategy: Disabled |
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